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//-----------------------------------------------------------------------------
//
// <copyright file="CompressEmulationStream.cs" company="Microsoft">
// Copyright (C) Microsoft Corporation. All rights reserved.
// </copyright>
//
// Description:
// Abstract base class that provides a fully functional Stream on top of different
// various compression implementations.
//
// History:
// 07/14/2004: BruceMac: Initial implementation.
// 12/06/2005: BruceMac: Split into abstract base class and move DeflateStream
// specific implementation into ManagedEmulationStream
// 12/16/2005: BruceMac: Reworked to move functionality into IDeflateTransform
// interface to avoid calling virtuals from constructor (FxCop rule)
//-----------------------------------------------------------------------------
using System;
using System.IO;
using System.IO.Compression; // for DeflateStream
using System.Diagnostics;
using System.IO.Packaging;
using System.Windows;
using MS.Internal.WindowsBase;
namespace MS.Internal.IO.Packaging
{
//------------------------------------------------------
//
// Internal Members
//
//------------------------------------------------------
/// <summary>
/// Interface for Deflate transform object that we use to decompress and compress the actual bytes
/// </summary>
interface IDeflateTransform
{
void Decompress(Stream source, Stream sink);
void Compress(Stream source, Stream sink);
}
/// <summary>
/// Emulates a fully functional stream using restricted functionality DeflateStream and a temp file
/// </summary>
internal class CompressEmulationStream : Stream
{
//------------------------------------------------------
//
// Public Methods
//
//------------------------------------------------------
#region Stream Methods
/// <summary>
/// Return the bytes requested from the container
/// </summary>
/// <param name="buffer">destination buffer</param>
/// <param name="offset">offset to write into that buffer</param>
/// <param name="count">how many bytes requested</param>
/// <returns>how many bytes were written into <paramref name="buffer" />.</returns>
/// <remarks>
/// The underlying stream, expected to be an IsolatedStorageFileStream,
/// is trusted to leave the IO position unchanged in case of an exception.
/// </remarks>
public override int Read(byte[] buffer, int offset, int count)
{
CheckDisposed();
PackagingUtilities.VerifyStreamReadArgs(this, buffer, offset, count);
return _tempStream.Read(buffer, offset, count);
}
/// <summary>
/// Seek
/// </summary>
/// <param name="offset">offset</param>
/// <param name="origin">origin</param>
/// <returns>zero</returns>
public override long Seek(long offset, SeekOrigin origin)
{
CheckDisposed();
long temp = 0;
switch (origin)
{
case SeekOrigin.Begin:
{
temp = offset;
break;
}
case SeekOrigin.Current:
{
checked { temp = _tempStream.Position + offset; }
break;
}
case SeekOrigin.End:
{
checked { temp = _tempStream.Length + offset; }
break;
}
default:
{
throw new ArgumentOutOfRangeException("origin", SR.Get(SRID.SeekOriginInvalid));
}
}
if (temp < 0)
{
throw new ArgumentException(SR.Get(SRID.SeekNegative));
}
return _tempStream.Seek(offset, origin);
}
/// <summary>
/// SetLength
/// </summary>
public override void SetLength(long newLength)
{
CheckDisposed();
_tempStream.SetLength(newLength);
// truncation always involves change of stream pointer
if (newLength < _tempStream.Position)
_tempStream.Position = newLength;
_dirty = true;
}
/// <summary>
/// Write
/// </summary>
public override void Write(byte[] buffer, int offset, int count)
{
CheckDisposed();
PackagingUtilities.VerifyStreamWriteArgs(this, buffer, offset, count);
// no-op
if (count == 0)
return;
_tempStream.Write(buffer, offset, count);
_dirty = true;
}
/// <summary>
/// Flush
/// </summary>
/// <remarks>Flushes to stream (if necessary)</remarks>
public override void Flush()
{
CheckDisposed();
if (_dirty)
{
// don't disturb our current position
long tempPosition = _tempStream.Position;
// compress
_tempStream.Position = 0;
_baseStream.Position = 0;
_transformer.Compress(_tempStream, _baseStream);
// restore
_tempStream.Position = tempPosition;
_baseStream.Flush();
_dirty = false;
}
}
#endregion Stream Methods
#region Stream Properties
/// <summary>
/// Current logical position within the stream
/// </summary>
public override long Position
{
get
{
CheckDisposed();
return _tempStream.Position;
}
set
{
CheckDisposed();
if (value < 0)
throw new ArgumentException(SR.Get(SRID.SeekNegative));
_tempStream.Position = value;
}
}
/// <summary>
/// Length
/// </summary>
public override long Length
{
get
{
CheckDisposed();
return _tempStream.Length;
}
}
/// <summary>
/// Is stream readable?
/// </summary>
/// <remarks>returns false when called on disposed stream</remarks>
public override bool CanRead
{
get
{
return (!_disposed && _baseStream.CanRead);
}
}
/// <summary>
/// Is stream seekable - should be handled by our owner
/// </summary>
/// <remarks>returns false when called on disposed stream</remarks>
public override bool CanSeek
{
get
{
return (!_disposed && _baseStream.CanSeek);
}
}
/// <summary>
/// Is stream writeable?
/// </summary>
/// <remarks>returns false when called on disposed stream</remarks>
public override bool CanWrite
{
get
{
return (!_disposed && _baseStream.CanWrite);
}
}
#endregion
#region Internal
//------------------------------------------------------
//
// Internal Methods
//
//------------------------------------------------------
/// <summary>
/// Constructor
/// </summary>
/// <param name="baseStream">part stream - not closed - caller determines lifetime</param>
/// <param name="position">current logical stream position</param>
/// <param name="tempStream">should be an IsolatedStorageFileStream - not closed - caller determines lifetime</param>
/// <param name="transformer">class that does the compression/decompression</param>
/// <remarks>This class should only invoked when emulation is required.
/// Does not close any given stream, even when Close is called. This means that it requires
/// another wrapper Stream class.</remarks>
internal CompressEmulationStream(Stream baseStream, Stream tempStream, long position, IDeflateTransform transformer)
{
if (position < 0)
throw new ArgumentOutOfRangeException("position");
if (baseStream == null)
throw new ArgumentNullException("baseStream");
// seek and read required for emulation
if (!baseStream.CanSeek)
throw new InvalidOperationException(SR.Get(SRID.SeekNotSupported));
if (!baseStream.CanRead)
throw new InvalidOperationException(SR.Get(SRID.ReadNotSupported));
if (tempStream == null)
throw new ArgumentNullException("tempStream");
if (transformer == null)
throw new ArgumentNullException("transformer");
_baseStream = baseStream;
_tempStream = tempStream;
_transformer = transformer;
// extract to temporary stream
_baseStream.Position = 0;
_tempStream.Position = 0;
_transformer.Decompress(baseStream, tempStream);
// seek to the current logical position
_tempStream.Position = position;
}
#endregion
//------------------------------------------------------
//
// Protected Methods
//
//------------------------------------------------------
/// <summary>
/// Dispose(bool)
/// </summary>
/// <param name="disposing"></param>
/// <remarks>We implement this because we want a consistent experience (essentially Flush our data) if the user chooses to
/// call Dispose() instead of Close().</remarks>
protected override void Dispose(bool disposing)
{
try
{
if (disposing)
{
if (!_disposed)
{
Flush();
_tempStream.Close();
_tempStream = null;
// never close base stream - we don't own it
// _baseStream.Close();
_baseStream = null;
_disposed = true;
}
}
}
finally
{
base.Dispose(disposing);
}
}
/// <summary>
/// Call this before accepting any public API call (except some Stream calls that
/// are allowed to respond even when Closed
/// </summary>
protected void CheckDisposed()
{
if (_disposed)
throw new ObjectDisposedException(null, SR.Get(SRID.StreamObjectDisposed));
}
#region Private
//------------------------------------------------------
//
// Private Variables
//
//------------------------------------------------------
private bool _disposed; // disposed?
private bool _dirty; // do we need to recompress?
protected Stream _baseStream; // stream we ultimately decompress from and to in the container
protected Stream _tempStream; // temporary storage for the uncompressed stream
IDeflateTransform _transformer; // does the actual compress/decompress for us
#endregion
}
}
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